Wire seal, particularly for use in incandescent lamps and discharge tubes



March 10, 1942.

l -L-liLEMMENS A 2,276,218

WIRE SEAL PARTICULARLY FOR USE IN INCANDESCENT LAMPS AND DISCHARGE TUBESFig.1.

Filed June 15, 1940 5 mmD His A1: torneg.

-wire thickness is about 0.03 millimetre.

Patented Mar. 10,- 19 42 UNITED STATES PATENT- OFFICE WIRE SEAL,PARTICULARLY FOR USE'IN IN CANDE SCENT TUBES Hendricus Johannes Lemmens,Eindhoven, Neth- LAMPS AND DISCHARGE erlands, assignor to GeneralElectric Com- Application June 15, 1940, Serial No. 340,829 In theNetherlands May 27, 1039 8 Claims. (c1. 49-92) also been suggested toseal band-shaped metal in layer may be used than in the case of a metalsuch as molybdenum. A tungsten wire will be chosen for example when theseal is. to be given a high thermal load; in this casexuse'is made ofthe fact that tungsten has a very high melting point and does notvolatilise rapidly.

If molybdenum is used as the wire material the layer of quartz orquartz-glass fused to the wire It has quartz but again the thickness ofthis band is but,

The known seals are therefor only suitable for use at comparatively lowcurrent strengths and if a seal is desired for higher current strengthssomewhat complicated solutions must be resorted to, use being made, forexample, of a plurality of j seals connected in parallel or the like.This renders the use of such seals rather expensive whilst themanufacture oftenentais difficulty and requires operators of high skill.

The invention provides means permitting of obtaining a very reliableseal which, owing to the fact that wires of very considerable thickness,for example of a few millimeters, can be sealed, may also be used forcomparatively high current strengths.

In the seal according to the invention the wire is made of a materialhaving a melting point exceeding 2000 C., has a diameter D of at least0.05 mm. and has a layer of quartz or quartz-glass fused to it, thethickness of the layer being not more than 0.24 mm. with wirethicknesses of less than 0.6 mm. and not more than 024+ ('D- 0.6) 0.16mm. for wire-thicknesses exceeding 0.6 mm.

r The invention is based on recognition of the fact that seals whichremain gas-tight at high temperatures even after a long time ofoperation, and in which comparatively thick wires are sealed into quartzcan be obtained if care is taken that the film of quartz or quartz-glassisvery thin compared with the wire.

The value indicated above for the thickness of the quartz orquartz-glass layer on the wire is a maximum value. If thelayerathickness is chosen in accordance with the maximum admissiblevalue a seal is obtained which, although a certain wastage occurs inmanufacture, satisfies all requirements when in use and continues tosatisfy them and notably does not manifest the defect of known seais ofeventually losing gas-tightness.

In the case of a metal such as tungsten a thicker preferably has athickness d of not more than 0.24 mm. with wire thicknesses D less than0.6 mm; and a thickness of not more than 024+ (D-0.6)0.l6 0.8 min. forwire thicknesses exceeding 0.6 mm.

Molybdenum is preferably chosen as the ma: terial for the wire if asmall evolution of. heat, resulting from the heat evolved in the .wire,is desired or because of further treatment.

Apart from molybdenum and tungsten other metals, alloys and compoundshaving a melting point higher than 2000 C. may naturally be used for thewire in the seal. Thus, for example, tantalum may be'mentioned.

The seal described above is of value if it is desired for any reason tohave a wire of a metal having a melting point higher than 2000 C. towhich an insulating film is fused, for example if the occurrenceof'flashing-over between two electrodes is to be avoided in a dischargetube; in this case one of the electrodes or both may be provided withthe layer according to the invention.

The seal according to the invention is con- 'veniently made with the'aidof a quartz tube.

invention is of great importance in connecting with the attachment ofmetal wires of the abovementioned kind and dimensions to a bulb of anelectric incandescent lamp or discharge tube. For this purpose thequartz layer of the seal may have a glass or quartz bead fused to it.The choice of the material of thebead depends inter alia on the materialof the bulb.

It is preferable with such a lamp or discharge tube that the part of thebulb which is immediately adjacent a seal should be substantially normalto the Wire.

The seal according to the invention when equipped with a bead can beused by itselfjor various purposes. Thus, for example, such a bead canbe used as a support for metal members. For example the ears whichsupport the'filament of an electric incandescent lamp could be insertedin such a bead secured to a tungsten wire.

In order that the invention may be clearly understood and readilycarried into effect it will now be described more fully with referenceto the accompanying drawing.

Fig. l is a graph showing the relation that exists between a wirethickness D and an associated quartz layer having a thickness d, that isto say the graph indicates at each value of the wire thickness themaximum admissible thickness of the quartz or quartz-glass layer. Thewire thicknesses are plotted as abscissae, the layer thicknesses asordinates. The relation ,registered in the graph was ascertained byexperiment. The line ABC shows the relation which applies if tungsten oranother metal or alloy having a melting point exceeding 2000 C. ischosen as the material for the wire. Dots indicate those seals whichproved durable with tungsten sealed in quartz, whereas those seals,formed of the samematerials, which failed are denoted by circles. It isfound that the line ABC satisfies the following relation: d=0.24+(D-0.6) 0.16 mm.

From this graph it follows, for example, that with a tungsten wire of 2mm. thickness the maximum permissible thickness of the quartz layerfused to such a wire is 0.47 mm. For a wire thickness D= mm. thethickness of the quartz layer has a maximum value of 0.94 mm. It isobvious that the great advantage is obtained whenfollowing the rulegiven that even thick tungsten wires can be sealed into quartz.

It is found that it is generally undesirable to choose the maximumpermissible thickness for the thickness of a quartz layer to be fused toa metal wire since in this case wastage is liable to occur inmanufacture. Thus, it has been found -by us that when the wire to befused in the quartz is made of molybdenum, it is desirable that thethickness of the quartz layer should not be higher than d=0.24+(D-0.6)0.16X0.8 mm. This line is designated in the graph shown in Fig. 1 byABD.

Fig. 2 shows, on a larger scale, a seal according to the invention inwhich the tungsten wire I has a thickness D of 2 mm. In this case thethickness d of the layer 2 is 0.4 and this is slightly lower than themaximum permissible value of 0.47 as follows from the line ABC ofFig. 1. It is found that the quartz layer 2 is so firmly sealed on thetungsten wire that if attempts are made to break this seal it is morelikely that quartz fragments break from the quartz layer 2 than that theadhesion between the wire I and the layer 2 is disturbed.

the adhesion which occurs between the tube 4 and the wire 3 due to theheating operation. When the heating has been finished the lefthand partof the tube 4 is removed along the plane TI and the seal has thusassumed its final shape.

Fig. 4 shows a tungsten wire 5 having mounted on it a quartz layer 6 andon top thereof a glass Fig. 3 shows another method of providing-a whichis contained in the space R and in the annular space between the wire 3and the tube 4 is driven off so that it escapes at S. The oxide which isformed is also driven off and this prior to bead l. The figure showsthat the quartz layer 6 extends on either side of the glass bead. Thisprojecting portion may be removed, for example, by grinding but due tothe fact that the bead is made of material different from that of thelayer it is possible to ascertainthat the glass bead is applied tothemetal wire by way of an intermediate layer of quartz. In addition, thefact that the portion of the layer which extends from the bead is groundaway can be discerned due to the subjacent wire surface not being burnedat the area where the layer'is ground off, this burning being alwayspresent to a greater or less extent with the metal surface that has notbeen coated with quartz. This latter fact is due to the action of theflame used during sealing.

Fig. 5 again shows the tungsten wire of Fig. 4, the glass bead I mountedon the quartz layer 0 being, however, sealed to a glass wall I, forexample, the bulb of an electric incandescent lamp. The figure showsthat the portion of the lamp bulb which is immediately adjacent the sealis normal to the tungsten wire 5 existing in th seal.

What I claim is:

1. A gas-tight, electrically conducting seal comprising a metal wire anda layer of quartz fused to said wire, said wire having a melting pointhigher than 2000 C. and a diameter of at least 0.05 mm., the thicknessof the quartz layer and the diameter of the wire being in such relationthat the layer is not more than 024mm. thick when the diameter of thewire is less than 0.6 mm. and not more than 0.24+(D-0.6) 0.16 mm. thickwhen the diameter of the wire is greater than 0.6 mm. where D is thediameter of the wire.

2. A gas-tight, electrically conducting seal comprising a tungsten wireand a layer of quartz fused to said wire, said wire having a diameter ofat least 0.05 mm., the thickness of the quartz layer and the diameter ofthe wire being in such relation that the layer is not more than 0.24 mm.thick when the diameter of the wire is less than 0.6 mm. and not morethan 0.24+(D-0.6)0.16 mm. thick when the diameter of the wire is greaterthan 0.6 mm. where D is the diameter of the wire.

3. A gas-tight, electrically conducting seal comprising a molybdenumwire and a layer of quartz fused to said wire, said wire having adiameter of at least 0.05 mm., the thickness of.

0.24+ (D 0.6) 0.16X0.8 mm. thick when the diameter of the wire isgreater than 0.6 him. where D is the diameter of the wire. 4. Agas-tight, electrically conducting se comprising a metal wire, a layerof quartz fused to said wire anda head of vitreous material fused tosaid quartz layer, said wire having a melting point higher than 2000 C.and a diameter of at least 0.05 mm., the thickness of the quartz layerand the diameter of the wire being-in such relation that the layer isnot more than 0.24 mm. thick when the diameter of the wire is less than0.6 mm. and not more than 0.24+(D-0.6)0.16

mm. thick when the diameter of the wire is greater-than 0.6 mm. where Dis the diameter of the wire.

5. A gas-tight, electrically conducting seal for a vitreous envelopehaving a planar portion, said seal comprising a metal wire normal to theplanarportion of said envelope, a layer of quartz fused to said wire anda bead of vitreous material fused to said quartz layer for fusion withsaid envelope, said wire having a melting point higher than 2000 C. anda diameter of at least 0.05 mm., the thickness of the quartz layer andthe diameter of the wire being in such relation that the layer is notmore than 024mm. thick when the diameter of the wire is less than 0.6mm. and not more than 0.24+(D-0.6)0.l6 mm. thick when the diameter .ofthe wire is greater than. 0.6 mm. where D is the diameterof the wire. 7

6. A gas-tight, electrically conducting seal comprising a metal wire, alayer of quartz fused to said wire and a glass bead fused to said quartzlayer. said wire having a melting point higher than 2000 C. and adiameter-of at least 0.05 mm., the thickness of the quartz layer and thediameter of the wire being in such relation that the layer is not morethan 024mm. thick when the diameter of the wire is less than 0.6 mm. and

the diameter of the wire is greater than 0.6 mm. where D is the diameterof the wire.

7. A gas-tight, electrically conducting seal than 0.6 mm. where D is thediameter of the wire.

8. A gas-tight, electrically conducting seal comprising a tantalum wireand a layer of quartz fused to said wire, said wire having a diameter ofat least 0.05 mm., the thickness of the quartz layer and the diameter ofthe wire being in such relation that the layer is not more than 0.24 mm.thick when the diameter of the wire is less than 0.6 mm. and not morethan 0.24+(D-0.6) 0.16

'mm. thick when the diameter of the wire is greater than 0.6 mm. where Dis the diameter of the wire.

HENDRICUS JOHANNES LEMMENS.

, 3 not more than o.'24+ n-o.s) 0.16 mm. thick when.

